cars = 100 #定义一个变量
PI = 3.14159    # 定义一个表示圆周率的常量 Python没有内置的常量类型，但通常约定俗成的做法是大写变量名来表示常量。

space_in_a_car = 4.0
drivers = 30
passengers = 90
cars_not_driven = cars - drivers
cars_driven = drivers
carpool_capacity = cars_driven * space_in_a_car
average_passengers_per_car = passengers / cars_driven

print("There are", cars, "cars available.")
print("There are only", drivers, "drivers available.")
print("There will be", cars_not_driven, "empty cars today.")
print("We can transport", carpool_capacity, "people today.")
print("We have", passengers, "to carpool today.")
print("We need to put about", average_passengers_per_car, "in each car.")
print("", PI*3 )
print("", round(PI*3) )
print("", round(4.5) )#round() 函数在处理 .5 的情况时，会四舍五入到最近的偶数。这种做法被称为“银行家舍入”
print("", round(3.5) )
#用python编写一个简单的计算问题，以及round函数说明